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When I listen to CDs through my Eico HF-81, I hear severe HF distortions and excessive hiss and sibilance to the extent that I have to turn HF controls almost completely counterclockwise.
Vinyl records sound fine (I recently replaced old Mullard 12AX7 tubes of the phono pre-amp that produced hum with two NOS Mullard 12AX7 tubes and it is quiet now).
I don't have a tube tester but what should I check? Should I try to replace other tubes or look elsewhere (cables, resistors, etc.)?
I don't have pictures right now.
I have other amps each of which sounds much better than Eico when I want to listen to CDs, but I am just curious...
Follow Ups:
This would not be my #1 hypothesis, but is it possible that the output of your CDP is setting the HF81 into oscillation? Especially SACD has some very high frequency hash that is filtered out in many SACD players, but not all. For example, my Ayre C5Xe is not useable with my Beveridge direct-drive amplifiers; it drives them to nasty oscillation. Ayre conceded to me that they deliberately do not use a high-pass filter on the output of their SACD decoding circuit, because in their opinion, it sounds better without. In contrast, a Sony SACD player which does use a hi-pass filter on its output, works fine with the Bev amplifiers on SACD.On balance, though, I favor EStat's hypothesis.
Edits: 05/22/15
There is no such problem with my Eico ST-40 and Sansui AU-517 (which is my favorite)...
It may be...However, good quality CDs don't distort with HF-81.
is you are overloading the input. Many CDPs have very high output relative to that of yesteryear.
A GamuT CD-1 I used for about a decade had a 4V output (along with very low ouput impedance) which is why I bypassed my pre altogether and used DIY attenuators.
see if you can find the output voltage in the manual.
Or you can go to radioshack (if you can find one) and build a cheap but good attenuator.
15k 1/4 watt metal film in line with a 100k volume pot shunt to ground. Very simple.
There is another possibility - the seller who upgraged this amp used silver wiring inside. I wonder why? Silver wires can make the amp sound thinner and exaggerate sibilance...
In addition, EL-84 tubes have more HF focus than, say, EL-34s, which may add to the problem.
I think the silver wire you are seeing is the 600v teflon coated wire. BTW excellent wire!
As for the EL84 vs EL34 differences, that is due to more of the amp design and component matching.
You can try this. Inside the amp put a 15K resistor in line with the CDP input signal and a 20k-ish resistor to it's ground. If that improves it even a little then you're on the right track.
that Cary he has is 3V out I think. Turn down the output level via the remote and see what happens. I'd put it at 50% at most and go from there.
E
T
It's quite possible - as far as I remember, my Cary 308T CD player has a very high output (though it has a volume control). I will probably experiment with another player if I have time...
Have you tried any other of the line level inputs?
I changed Aux A for Aux B and it seems that it sounds clearer. Not so good as vinyl, however (with this unit).
Looks like it reveals the limitations of CD sound...
OK, I'll try other line level inputs.
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